Brain-derived neurotrophic factor modulates cholesterol homeostasis and Apolipoprotein E synthesis in human cell models of astrocytes and neurons

In the central nervous system, cholesterol is critical to maintain membrane plasticity, cellular function, and synaptic integrity. In recent years, much attention was focused on the role of cholesterol in brain since a breakdown of cholesterol metabolism has been associated with different diseases. Brain-derived neurotrophic factor (BDNF) was previously reported to elicit cholesterol biosynthesis and promote the accumulation of presynaptic proteins in cholesterol-rich lipid rafts, but no data are available on its ability to modulate physiological mechanisms involved in cholesterol homeostasis. Major aim of this research was to investigate whether BDNF influences cholesterol homeostasis, focusing on the effect of the neurotrophin on Apolipoprotein E (ApoE) synthesis, cholesterol efflux from astrocytes and cholesterol incorporation into neurons. Our results show that BDNF significantly stimulates cholesterol efflux by astrocytes, as well as ATP binding cassette A1 (ABCA1) transporter and ApoE expression. Conversely, cholesterol uptake in neurons was downregulated by BDNF. This effect was associated with the increase of Liver X Receptor (LXR)-beta expression in neuron exposed to BDNF. The level of apoptosis markers, i.e. cleaved caspase 3 and poly ADP ribose polymerase (PARP), was found increased in neurons treated with high cholesterol, but significantly lower when the cells were exposed to cholesterol in the presence of BDNF, thus suggesting a neuroprotective role of the neurotrophin, likely through its reducing effect of neuronal cholesterol uptake. Interestingly, cholesterol stimulates BDNF production by neurons. Overall, our findings evidenced a novel role of BDNF in the modulation of ApoE and cholesterol homeostasis in glial and neuronal cells.